Description: Doing plenty of mentally-stimulating activities -- such as playing chess, reading a newspaper, or attending a play -- in old age helps reduce the risk of Alzheimer's disease, according to a study of more than 700 elderly Americans. The Chicago residents, who averaged 80 years of age at the start of the study, underwent annual cognitive testing for up to five years. During the study, 90 people developed Alzheimer's disease, and 102 died.